Vault Condition: On 30 Oct 1992 the very short-period seismometers (Geotech Model GS-13) were relocated in a surface vault approximately 100 meters distant from the borehole. The seismometers are located on a concrete floor poured on top of exposed granite rock. Vault is covered with about 1 meter of earth. Temperature and humidity are stable, however, strong winds cause high frequency background noise. Prior to this time the very short-period system was located in the vault which was used for the ALQ seismograph system. Please note that the coordinates and elevation for this vault are slightly different. This information can be found in the listing for station

Site Geology: Pensylvanian and later sediments overlying a peneplained Pre-Cambrian complex of metasediments and granitic intrusives. Borehole is drilled through 6 meters of alluvial overburden and 94 meters of fractured granite.

As part of the annual calibration process, the USGS runs a sequence that includes a random, a step, and several sine wave calibrations. The USGS analyzes the random binary calibration signal in order to estimate the instrument response. The figures below show the results from the analysis of the most recent processed calibration at the station.

We use an iterative three-step method to estimate instrument response parameters (poles, zeros, sensitivity and gain) and their associated errors using random calibration signals. First, we solve a coarse non-linear inverse problem using a least squares grid search to yield a first approximation to the solution. This approach reduces the likelihood of poorly estimated parameters (a local-minimum solution) caused by noise in the calibration records and enhances algorithm convergence. Second, we iteratively solve a non-linear parameter estimation problem to obtain the least squares best-fit Laplace pole/zero/gain model. Third, by applying the central limit theorem we estimate the errors in this pole/zero model by solving the inverse problem at each frequency in a 2/3rds-octave band centered at each best-fit pole/zero frequency. This procedure yields error estimates of the 99% confidence interval.